Angular Contact Bearing Confusion

[skipper]

Hi All,

well I have read hundreds of post and looked at many pictures and I still cannot figure out how to mount angular contact bearigs. So, I made up a drawing of what I am confused about. I hope it is clear, A and B version. On A, I have seen shims that are placed between the two AC bearings and a thrust washer to squeeze everthing only on the inside races? The bearings are recessed into the mount.

On B, there is no shims, the bearing mate against each other. The bearing portrude out of the mount and a big thrush washer squeezes the entir bearing surface.

Does this make sense?
Do I have it right?
How much torque for the preload?
Does anyone have good detailed schematics or pictures to add to help me?
Does the nut and thrush washer rotate with the shaft?

Thanks for the help
Rene

[NC Cams]

Both are/can be viable DEPENDING on the way the bearings are/were preloaded.

Typically, the pairs are ground for DB, or DF mounting. they can be univesally ground for DB, DF and/or DT mounting - google as needed to figure out what DB, DF and/or DT stand for.

Due to the low and inconsistant friction of ball bearings, totating torque is a poor (at best), invalid (most likely) method for establishing preload. The typical/best/traditional method is raceway offset amount - the amount of force needed to shove the inner raceway sides back to being "flush" with the outer raceway sides is the preload.

The raceway sides are gound with a certain amount of width difference so that when the raceways are clamped solid and flush, the desired/preprogrammed preload is established.

Due to variations in raceway geometry, offsest vary from manufacturer to manufacturer. Hence, a 10 micron offset for 1 bearing won't be the same preload in ALL of them.

When the nut is tight and the deal is all preloaded to the programmed amount, the outer rings ALL touch first and at the point the inner rings and nut and ball screw are all solidly clamped, the inners all rotate in unison (DB mount) - the outers are clamped by end clamps/plates on the housing

In DF mount, the inner rings touch first and preload is met/established when the outer rings are clamped until the outer rings touch.

[svenakela]

You're the man NC!
But to mess it up even more, this is the way my bearings are mounted.

Regards,
Sven

[skipper]

Thanks Guys,

that make things more clear. Do you have any idea of the thinkness of the spacer between each bearing. .005, .010? How much to torque the nut?

Thanks again,
rene

[NC Cams]

Skipper: how much to torque the nut? I dunno nor do I care in the example cited and here's whY:

When you are NOT using true/fixed bearing offset to establish preload, you adjust preload by how much you tighten the nut. The ONLY way to determine the preload is to do a torque/turn/raceway offset MEASUREMENT - with the info and equipment the average DIY guy has, you simply can NOT calculate the torque vs preload value.

The CLASSIC, industry standard method is to apply a force to the rings in line with the contact and thrust application angle, measure the offset vs force and then flush grind the rings with this offset in mind. This way, when you assemble the bearings and tighten them flush, you have the desried and established preload. NO bearing spacers between the bearings whatsoever are needed if/when it is done properly.

IF spacers are needed, equal thickness (as in EXACTLY equal) spacers are used between BOTH inner and outer rings simply to make the bearings "wider". This affects a wider stance between Front and Rear bearing or to make up space for some wierd, non standard width bearing that the machine maker crafted up.

By using a user adjustable method per the illustration, the user is responsible for some how crafting up the preload - lame method for doing so accurately and/or repeatably for reasons already cited. This alllows TOO much potential for kluging and indiscriminate tinkering - and/or perhaps even excessive loading of the A/C's.

The industry preferred method of preloading A/C's is to incorporate a fixed/offset grind.

KAF Mfg in Stamford CT does this sort of work. Send them your bearings, give them the preload desired, pay them what they ask and then simply install them with no shims or other crap and/or user adjustable schemes.

[runchman]

Here is a link from SKF that has a lot of angular contact info, I found it interesting while going through my intensive reading of angular contact stuff, maybe you will too:

http://www.skf.com/portal/skf/home/p...&newlink=1_3_2

I ended up buying a set of 'bearings for universal matching' that don't require a spacer or shims. Seemed like a reasonable choice, we'll see once I get my clausing conversion done...

- John

[NC Cams]

The SKF site referenced above explains a lot but it is lacking with regard to the specific HOW"s and WHY"s of A/C preloading. I'm pretty sure that other bearing sites show the concept in a better, more understandable way.

NSK and Barden had some real simple/easy to understand sketches that outlined the concept - a self aflicted web search should find them for you. The NSK explanation, at one time, give much better insight into why to use DB over DF and/or DT - there are reasons.

DB gives best overturning moment resistance, DF gives best self alignment (good for Ball screws over long lengths), DT gives added capacity due to stacking of bearings and more bearings in parallel to absorb/share the applied load.

The key to REALLY understanding A/C's is to study the drawings and figuring out the load paths along the way. Once you do, the mounting process will become self evident. Sadly, the preloading may need the aid of professional rework facilities. Not ALL bearing modifications are necessarily DIY capable....

[svenakela]

I think your right, there are probably washer at both inner and outer, but I'm sure my bearings are mounted with the inner races "poiting" outwards.

Regards,
Sven

[Nami]

http://www.bardenbearings.com/PDF%20CD/PB11.PDF

[Oldmanandhistoy]

Originally Posted by Nami http://www.bardenbearings.com/PDF%20CD/PB11.PDF

Thanks Nami